Viral hepatitis, caused by the six hepatotropic viruses, viz, hepatitis A virus (HAV) hepatitis B virus (HBV), Hepatitis D virus (HDV), hepatitis E virus (HEV) and hepatitis G virus (HGV), represents a major health problem world wide. Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV) are the major cause of devastating liver diseases all over the world. Recent estimates indicate that more than 500 million people appeared to have been infected by these liver-tropic viruses. With about 180 million people currently infected worldwide, HCV represents a daunting public health problem. Out of these, at least 15-20 million in India and about 4 million people in the USA suffer from chronic infection by HCV. In some countries like Egypt about 10 to 15 per cent of general population appears to carry HCV. More than 30 to 40% of the infected people develop liver cirrhosis and/or hepatocellular carcinoma after suffering with chronic infection for a decade or two and therefore HCV infection is considered to be a silent killer. Although interferon a in combination with ribavirin work well with some patients infected by some genotypes, more than 50% of the patients are refractory to such treatment.
Non-A, Non-B hepatitis (NANBH) are transmissible diseases that are believed to be viral induced, and that are distinguishable from other forms of viral-associated liver diseases, including that caused by the known hepatitis viruses. Viral hepatitis, caused by the hepatotropic viruses, viz, hepatitis A virus (HAV) hepatitis B virus (HBV), Hepatitis D virus (HDV), hepatitis E virus (HEV) and hepatitis G virus (HGV), represents a major health problem world wide. Until recently there has been neither clarity nor agreement as to the identity or specificity of the antigen antibody systems associated with agents of NANBH. It is possible that NANBH is caused by more than one infectious agent and unclear what the serological assays detect in the serum of patients with NANBH.
In 1987, Houghton, et al. cloned the first virus definitively linked to NANBH. Houghton et al. described there in the cloning of an isolate from a new viral class, hepatitis C virus (HCV), the prototype isolate described therein being named “HCV 1”. HCV is a Flavi-like virus, with an RNA genome. They described the production of recombinant proteins from HCV sequences that are useful as diagnostic reagents, as well as polynucleotides useful in diagnostics hybridization assays and in cloning of additional HCV isolates.
Hepatitis C virus (HCV) has emerged in recent years as the leading cause of worldwide blood-transmitted chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma A vaccine to prevent HCV infection has not yet been available any where in the world and the existing antiviral treatments are ineffective in the majority of the HCV infected patients.
Despite significant progress in the field of biotechnology, reliable diagnostic procedures, an alternative animal model other than chimpanzee, efficient cell culture systems that can support long-term replication of the virus and effective therapeutic strategies are still lacking.
As with any disease, an accurate diagnosis of HCV infection is essential before patients are counseled and treatment is initiated. Since, the identification and molecular characterization of the HCV in 1989 by Choo and colleagues, a number of diagnostic tests based on the detection of either the anti HCV antibodies or HCV-RNA by PCR in patient sera have been developed.
Presently, a third generation ELISA that incorporates antigens from the Core, NS3, NS4 and NS5 proteins of HCV, representing about 60% of the total amino acid sequence of HCV polyprotein, is available in the market. Although, this ELISA is significantly sensitive, a major drawback of this assay is that it fails to differentiate between active and post infection cases. In addition to this, it is now well documented that the commercially available third generation ELISA can not be used to detect all the viral infections in Indian patients owing to genotype sequence variations.
It may be noted at this stage that the commercial 3rd EIA is based on genotype 1 (other than Indian HCV strain) and genotype specific antibody response in this virus is now documented. Hepatitis, Cirrhosis and Hepatocellular carcinoma, caused by Hepatitis C Virus remain a global health problem and development of a vaccine to prevent this silent killer is of utmost priority. Every major country's goal is to produce a therapeutic vaccine for those 180 million people who are already infected by HCV and a preventive vaccine to eradicate future HCV infections. Just a few years ago, there was a lot of skepticism about the possibility of developing a viable vaccine for HCV. The situation, however, has changed in the last two to three years mainly because i) about 40 to 50% of the patients spontaneously recover from infection, implying that their immune system can fight off the virus; ii) infected chimpanzees (the only animal model available for HCV produced viremia) and convalescent humans are protected against the re-exposure; and iii) chronically infected patients improved their immune response and liver functions when the viral envelope protein E1 was administered as therapeutic vaccine.
Luckily for Hepatitis B, there is a preventive vaccine available in most of the countries; thus, future infections can be prevented. A therapeutic vaccine for HBV to boost the immunity of the infected people may be forthcoming. Unfortunately such a vaccine is not available for HCV any where in the world. Because of the propensity of the virus to undergo genetic variation, resulting in the evolution of quasispecies, a vaccine developed in the western countries will not be effective in India. For that matter, a vaccine developed against the strain(s) prevalent in Northern India may not be effective in South India. Therefore, controlling HCV infection is a challenging task. With the recent breakthroughs in research and development on HCV, there is a lot of optimism now about the development of at least a therapeutic and a potential preventive vaccine. The major problem, however, is that a single vaccine may not be suitable for every country as there are several different genotypes. In India genotypes 1 and 3 are more prevalent, which are quite different from genotypes existing in other regions of the world. Therefore, our major goal is to make the vaccine candidate proteins, E1 and E2 for both genotypes in yeast and/or animal cells and test for their efficacy as therapeutic and preventive vaccines. We already know the sequence of these genotypes and we have also completed cloning of the genes encoding E1 and E2 proteins. Now, the major goal of this project is to make these proteins in large quantities, purify and characterize, and carry out human trials.
There is an ever-increasing demand for sensitive and accurate tests for detection and screening of Hepatitis viral carriers. There is also a need for effective vaccines and therapeutic agents for preventing and treating viral hepatitis. Moreover, there is tremendous genetic variation among existing strains from each country and thus development of potential vaccines depend upon characterization of the strian (s) existing among Indian population.
To overcome the problems associated with the prior art, the applicant has cloned and sequenced the genome of a novel Indian strain of HCV. This sequence can be used to develop HCV antigens, diagnostic kits and therapeutic vaccines.